1. Field of the Invention
The present invention relates to a novel cyclobutenedione derivative that is advantageous to serve as a non-linear optical material, a manufacturing method therefor and a non-linear optical device using the same.
2. Description of Related Art
In the fields of optical communication and optical information process, non-linear optical devices play important roles. Non-linear optical materials for use in the non-linear optical devices are a significantly important substance for realizing optical signal processing, such as photomixing for generating the frequency which is the sum of or the difference between two types of incident light beams having different frequencies, optical parametric generation, with which the frequency of a new generated lightwave is parametrically dependent on that of an original light source, the Pockels effect and the Kerr effect obtainable due to change in the refractive index of an optical medium, conversion of incident light into the second harmonic component (SHG) or the third harmonic component (THG) and a memory effect obtainable from optical bistability.
Hitherto, inorganic compounds have been employed as the material for the non-linear optical devices of the foregoing type. Although crystal of inorganic compounds, such as potassium titanium phosphate (KTP: KTiOPO.sub.4) and lithium niobate (LN: LiNbO.sub.3), has been known, characteristics required to realize the foregoing purposes have not been satisfied.
On the other hand, organic non-linear optical materials have attracted attention in recent years as new optical device materials in the optoelectronic industrial field and, thus, the materials have energetically been developed and researched. In particular, compounds of a type having electron donative groups and electron accepting groups in their .pi. electron conjugated system have been known to have strong optical non-linear characteristic, at the molecule level, due to the interaction of the laser beams as electromagnetic waves and .pi. electrons locally present in the molecules.
There have been researched, for example, 2-methyl-4-nitroaniline, m-nitroaniline, N-(4-nitrophenyl)-L-prolinol, 4-dimethylamino-4'-nitrostilbene and 4'-nitrobenzylidene-4-nitroaniline.
These materials are, similarly to inorganic materials, usually used in a single crystal state. In order to exhibit secondary non-linear optical effect in this state, it is essential that the materials do not have centrally symmetric property. However, the great dipole moment of the molecule raises a problem in that non centrally symmetric crystal cannot easily be formed as a thermodynamically stable phase.
Although a fact has been known that employment of asymmetric center and use of hydrogen bonds are effective when a material which can grow into non centrally symmetric crystal is designed, a general method has not been found yet.
Organic crystal cannot easily be allowed to grow largely and obtained organic crystal is too brittle, which are peculiar issues for organic substances; therefore, there is also a problem in that precise and fine process cannot easily be performed. Thus, there arises a requirement for a high performance material necessary to manufacture efficient devices.
In general, the non-linear optical device material is required to have great optical non-linear characteristic, excellent processability, heat resistance, stability against environment, light transparency, high dielectric breakdown voltage and stability when irradiated with a laser beam. However, conventional materials cannot satisfy these requirements.
Accordingly, the inventors of the present invention suggested cyclobutenedione derivatives represented by the following General Formula (VI) and a non-linear optical device containing the same (JP-A-3-112950). Although the suggested derivatives have a greater optical non-linear characteristic as compared with conventional materials, a further improved material having great optical non-linear characteristic has been required.
As other prior art, the following are know: JP-A-7-309818 and JP-A-7-309819, in which systhesizing method of the compound which might be similar to the compound (X) referred to in the present invention and its property are disclosed; and JP-A-8-119914, in which disclosed are the synthesizing method of the compounds (III), (V) and (VII) referred to in the present invention and properties. ##STR1##